Micro-fluid ejection heads are useful for ejecting a variety of fluids including inks, cooling fluids, pharmaceuticals, lubricants and the like. A widely used micro-fluid ejection head is an inkjet print head used in an ink jet printer. Ink jet printers continue to be improved as the technology for making their micro-fluid ejection heads continues to advance.
In the production of conventional thermal ink jet print cartridges for use in ink jet printers, one or more micro-fluid ejection heads are typically bonded to one or more chip pockets of an ejection device structure. A micro-fluid ejection head typically includes a fluid-receiving opening and fluid supply channels through which fluid travels to a plurality of bubble chambers. Each bubble chamber includes an actuator such as a resistor which, when addressed with an energy pulse, momentarily vaporizes the fluid and forms a bubble which expels a fluid droplet. The micro-fluid ejection head typically comprises an ejector chip and a nozzle plate having a plurality of discharge orifices formed therein.
A container, which may be integral with, detachable from or remotely connected to (such as by tubing) the ejection device structure, serves as a reservoir for the fluid and includes a fluid supply opening that communicates with a fluid-receiving opening of a micro-fluid ejection head for supplying ink to the bubble chambers in the micro-fluid ejection head.
During assembly of the micro-fluid ejection head to the ejection device structure, an adhesive is used to bond the ejection head to the ejection device structure. The adhesive “fixes” the micro-fluid ejection head to the ejection device structure such that its location relative to the ejection device structure is substantially immovable and does not shift during processing or use of the ejection head. The bonding and fixing step is often referred to as a “die attach step.” Further, the adhesive may provide additional functions such as serving as a fluid gasket against leakage of fluid and as corrosion protection for conductive tracing. The latter function for the adhesive is referred to as part of the adhesive's encapsulating function, thereby further defining the adhesive as an “encapsulant” to protect electrical components of or used with the micro-fluid ejection head, such as a flexible circuit (e.g., a TAB circuit) attached to the micro-fluid ejection head.
However, the micro-fluid ejection head and the ejection device structure typically have dissimilar coefficients of thermal expansion. For example, micro-fluid ejection heads may have silicon or ceramic substrates that are bonded to an ejection device structure that may be a polymeric material such as a modified phenylene oxide. Thus, the adhesive must often accommodate both dissimilar expansions and contractions of the micro-fluid ejection head and the ejection device structure, and be resistant to attack by the ejected fluid.
Conventional adhesive materials tend to be non-flexible and brittle after curing due to high temperatures required for curing and relatively high shear modulus of the adhesive materials upon curing. Such properties may cause the adhesive materials to chip or crack. It may also cause the components (e.g., micro-fluid ejection head and/or ejection device structure) to bow, chip, crack, or otherwise separate from one another, or to be less resilient to external forces (e.g., chips may be more prone to crack when dropped). For example, during a conventional thermal curing process, the ejection device structure typically expands before a conventional die bond adhesive material is fully cured. The diebond material thus moves with the expanding device structure, wherein the diebond material cures with the device structure in an expanded state. Upon cooling the device structure, the device structure contracts and, with a rigid, cured diebond material, induces high stress onto the ejection head to cause the aforementioned bowing, chipping, cracking, separating, etc. Among other problems, such events can result in fluid leakage and poor adhesion as well as malfunctioning of the micro-fluid ejection heads, such as misdirected nozzles. Moreover, attempts to make adhesive materials more flexible after curing often lead to adhesive materials that are less resistant to chemical degradation by the fluids being ejected.
Accordingly, a need exists for, amongst other things, a flexible adhesive composition that is curable at relatively low temperatures and that is suitable for use in assembling micro-fluid ejection head components, and particularly, for attaching micro-fluid ejection heads to ejection device structures.
With regard to the foregoing and other object and advantages, various embodiments of the disclosure provide a thermally curable adhesive composition for attaching a micro-fluid ejection head to a device wherein the adhesive has a relatively low shear modulus upon curing. Various exemplary embodiments also provide a micro-fluid ejection head having an ejector chip and a thermally curable adhesive attached thereto, the adhesive having a shear modulus of less than about 10 MPa at 25° C., wherein “MPa” stands for “MegaPascals” (i.e., 1.0×106 Pascals).
Additionally, embodiments provide a micro-fluid ejection device having an ejector chip and a thermally curable adhesive attached thereto, the adhesive having a glass transition temperature of less than about 65° C. Various other embodiments provide a method for attaching a micro-fluid ejection head to a device. One such method includes attaching the head to a device with a thermally curable adhesive with a relatively low shear modulus dispensed between the head and the device, and curing the adhesive composition to provide the micro-fluid ejection device.
Advantages of the exemplary embodiments may include, but are not limited to, a reduction in ejector chip substrate bow, an increase in ejector head durability, increased planarity of the ejector head, and the like. Other advantages might include the provision of adhesives having improved mechanical, adhesive, and ink resistive properties. Reduced stresses may be present in the ejector head substrates due to the presence of improved adhesives according to the disclosed embodiments.